The visual inspection of a generator field and stator should be performed on a periodic basis. Conventional generator/stator inspection and testing procedures typically require the complete disassembly of the stator and the removal of the generator field from the stator before any inspections or tests can be performed on the unit. The cost of the disassembly and the removal of the field, the time it takes for this process, and the dangers of field removal have led to the occasional omission of the generator and stator examinations from outage schedules.
In-situ inspections of generators have been performed employing poles, trolleys, and field turning techniques. These procedures have not accomplished the inspection task in a satisfactory manner.
Miniature air gap inspection crawlers are disclosed in commonly owned U.S. Pat. Nos. 5,650,579 and 6,100,711, the contents of which are hereby incorporated by reference. These crawlers are designed to pass through the radial air gap between the core iron and the retaining ring for in-situ inspection of the field and stator core.
Video cameras and other inspection tools attached to the crawler may be used to perform generator field and stator core inspections. For example, a high-resolution video camera provides the operator with a clear view of the stator core laminations, stator wedges, field wedges, and the in-board ends of the retaining rings. The device thus provides detection capability for loose stator wedges, vibration bar sparking, core lamination damage due to foreign objects, motoring and hot spots, field wedge arcing, and surface heating damage. Through the generator in-situ inspection, information is gathered on the condition of the generator that can help determine if field removal is necessary.
Although these known devices are adequate for visual inspection, these visual systems cannot detect internal defects such as cracks or pits in the field teeth. Rather, such cracks can only be found by ultrasonic inspection. Currently, however, the rotor must be pulled out of the stator before an ultrasonic inspection can be performed.
There is a desire therefore for a device and method to perform in-situ ultrasonic inspection of a generator stator and field. The device preferably should be sized to pass through the radial air gap.